On 08/10/13 13:52, Enrico Gallo wrote:
Dear Micha, dear list,
2013/10/3 Micha Silver<[email protected]>
On 03/10/2013 12:42, Enrico Gallo wrote:
Dear list,
when using (GRASS 6.4.3) v.distance -a , points to lines, you get:
1. [output] vector theme, with no attribute table, with N elements
2. [table] , with N rows, optionally with source and target cat
Any idea about joining the two outputs without spatial join?
You probably want to look at the "upload=..." parameter
the problem is a bit more complex than using the "upload" parameter, IMHO
when using v.distance looking for all possible connections (not only
the nearest one)
v.distance -a from=vector_from to=vector_to output=connector
upload=cat,dist column=cat_to,distance table=connector_attributes
we get
- a vector output with connecting lines
- an output table with from_cat [by default], cat_to& distance
fields, completely populated
the output table seems to me a perfect attribute table for vector
output, but no common field is given to join the two:
Adding a table (v.db.addtable) and updating the cat field (v.to.db,
cat) of vector output doesn't solve, as I am not able to add an
autoincrement field in output table to perfom a join, without direct
SQL tricks.
Connecting the given output table (v.db.addtable) and then updating a
cat field, doesn't help even, because v.to.db uses an "INSERT"
statement with cat option , not the usual "UPDATE", so you have N
records with no cat + N records with cat but without attributes.
In both cases we are assuming the two "outputs" have the same order
for elements , but I don't know how much robust is this assumption!
But without a robust join, any spatial analysis of connecting lines is
almost impossible...
I am missing something trivial to bypass this impasse?
No, what you are trying to do seems quite obvious, but is not
implemented in v.distance AFAIK. I think you should file an enhancement
request. I agree that being able to link the table resulting from -a to
the vector map would be a nice addition.
Moritz
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